Out of the Box, no there isn't a way to do that, but thinking out of the box you can enter all of the needed Nexus id numbers in the new mod category and clear out all the id numbers from the other categories. This will allow new mods to go to that category. You can then do the right click set category and set primary category to assign them later on. Sort of a six of one, half a dozen of another fix.
This is a hack and worked in my test. No telling if it will break anything.

wrote a simple script "cat.py"
(needs python (version 2.7): http://www.python.or...ython-2.7.6.msi)
It goes through all .meta files (in the same directory) and changes the categoryID to a new one. Just copy all .meta's that should be changed in a seperate directory together with cat.py and run the script.
And use it with care! It creates backups, but hasn't been tested that much yet.

Attached Files

MT. GREAT. It looks as if the hard work with SASTEP pays off. Could be rather useful for some ppl. Why not create a normal thread in the main forum in which you announce this small util. Here it will likely be rather invisible. Not sure if this util makes changes quicker then doing it manually with the MOGUI or GSDFan's hack but it is certainly appreciated. Keep up the good work.

I will (iim)patiently wait.
I've looked at the NMM importer and its amazing how many things you get for free. The hard work like creating a new mod in the NMM importer and filling it is already done by the MO API. You also have access to all kinds of info from MO. Haven't delved in deep enough to know if some info is missing. But as Tannin stated, if something is missing it can/will be added if needed (sounds perfect). Parsing the installog.xml of NMM is a snap btw. Curious how easy it will be to create an XML file based upon the current enabled/installed mods. (creating it manually or by using an XML marshaller/unmarshaller (serializes stuff). If easy this would mean 'potential' for another kind of SASSTEP/ASI, namely a purely MO plugin based.